A number of rare earth-iron alloys have been developed which exhibit desirable magnetostrictive properties as described, for example, by Savage et al. in U.S. Pat. No. 4,308,475 which issued Dec. 29, 1981. The alloys described therein (e.g., Tb-Dy-Fe alloys) have been found to be useful in magnetostrictive transducers, delay lines, variable frequency resonators and filters.
Another group of alloys based on rare earth-iron-boron compositions is described in U.S. Pat. No. 4,612,047 issued Sep. 16, 1986 and by Seon et al. in U.S. Pat. No. 4,636,353 issued Jan. 13, 1987. The alloys (e.g., Nd-Fe-B) exhibit highly desirable magnetic properties for use as permanent magnets.
The commercialization of these rare earth/iron alloys has progressed to the point that relatively large quantities of rare earth/iron alloy scrap have been generated from the various manufacturing operations used to fabricate the alloys into suitable magnet components, electrical components and the like. The rare earth/iron alloy scrap generated by these fabrication operations varies considerably in form from dry, bulky, relatively large scrap pieces to a fine powder or dust referred to as "swarf". The bulky scrap pieces are produced primarily from casting and fabricating operations, while the swarf is produced primarily from abrasive cutting and grinding operations.
Industries that fabricate rare earth/iron alloys into articles of manufacture require some method to dispose of the rare earth/iron scrap and recover the alloy for reuse. This is especially true in the case of the rare earth/iron swarf generated in the various fabrication operations.
There is a need to dispose of the rare earth/iron alloy scrap in a manner that allows recovery of the alloy in a condition of purity amenable for reuse in the manufacture of end-use articles (e.g., permanent magnets) without the need for further alloy purification. In particular, a treatment process is needed that allows recovery of the rare earth/iron alloy in a manner effective to remove tramp non-metallic impurities, such as oxygen, nitrogen, hydrogen and metallic impurities, such as Li, Na, Al, Si, Ca, Zn, Mg, etc., picked up by the alloy during the various fabrication operations. The tramp elements must be reduced to levels specified by manufacturers of end-use articles, such as permanent magnets.
An object of the present invention is to address these needs by providing a flux (slag) remelting method applicable to rare earth/transition metal (e.g., iron) scrap for recovering the alloy at a purity level acceptable for reuse in the manufacture of end-use articles.